In tape automated bonding (TAB) or flip chip bonding, for example, it has been widely conducted to deposit gold, copper, solder, nickel or multi-layered materials thereof at prescribed areas (electrodes) on a surface of a semiconductor chip having interconnects, thereby forming protruding connecting electrodes (bumps). Such bumps electrically connect the semiconductor chip with package electrodes or TAB electrodes. There are various methods for forming these bumps, including an electroplating method, vapor deposition method, printing method, and ball bump method. The electroplating method has become in wide use due to its relatively stable performance and capability of forming fine connections, in view of a recent tendency to increasing number of I/O terminals on semiconductor chips and to finer pitch.
The electroplating method includes a spurting or cup method in which a substrate such as a semiconductor wafer is positioned horizontally with a processing surface to be plated facing downward and a plating solution is spurted from below; and a dipping method in which the substrate is placed vertically in a plating tank and immersed in a plating solution, while a plating solution is supplied from a bottom of the plating tank and is allowed to overflow the tank. According to the dipping method of electroplating, bubbles that can adversely affect quality of plating are easily removed and a footprint is small. The dipping method is therefore considered to be suited for bump plating in which holes to be filled by the plating are relatively large and which requires a fairly long plating time.
Conventional electroplating apparatuses, employing the dipping method, are provided with a substrate holder which detachably holds a substrate, such as a semiconductor wafer, with its end and back surfaces sealed while its front surface (to-be-plated surface) is exposed. Such conventional apparatuses, perform plating of the surface of the substrate by dipping the substrate holder, together with the substrate held by it, in a plating solution, and have an advantage of easy release of gas bubbles.
Since a substrate holder with a substrate held is dipped in a plating solution, the substrate holder is required to securely seal a peripheral portion of the substrate so that the plating solution will not intrude into a back surface (non-plating surface) side. Accordingly, in a substrate holder which detachably holds a substrate between a pair of supports (holding members), for example, a sealing member is mounted to one support and the sealing member is brought into pressure contact with a peripheral portion of the substrate placed and held on the other support, thereby sealing a peripheral portion of the substrate.
With reference to such a conventional substrate holder, attempts have been made to avoid leakage of a plating solution or other liquid, as by optimization of a shape, fixing method, and the like of the sealing member, periodical (including per substrate) cleaning of the sealing member, periodical change of the sealing member, improvement of precision in pretreatments of a substrate (formation of a seed layer or a photo resist film), or minimization of error in setting of a substrate in the substrate holder as well as periodical realignment.
Due to deterioration of the sealing member, however, it is difficult to effect a complete sealing. Complete sealing is difficult especially in performing plating to embed a plated film into fine recesses, since a plating solution having a good permeability is generally used in such a plating so that the plating solution can easily and fully permeate into the fine recesses. On the other hand, it is also generally difficult to detect leakage of plating solution or other liquid. Once leakage of plating solution occurs, the plating solution, which has leaked into a substrate holder, adheres to a back surface of a substrate, and the plating solution adhering to the substrate will transfer to a substrate transport device, resulting in staining of the entire apparatus with the plating solution. In addition, leaked plating solution can corrode an electrical contact, thereby preventing feeding of electricity.
When performing electroplating of a substrate held by a substrate holder, it is necessary to electrically connect the substrate to a negative pole of a power source. Accordingly, positioned e.g. inside a sealing member and in a region sealed with the sealing member, there is provided an electrical contact for electrically connecting the substrate to an external wire extending from a power source.
A known such electrical contact includes a metal contact plate of e.g. stainless steal having a horseshoe-shape cross-section, and a coil spring for biasing the metal contact plate toward a substrate. When the substrate is held by the substrate holder, one leg of the metal contact plate positioned on an outer side contacts an external wire through elastic force of the coil spring, while another leg of the metal contact plate positioned on an inner side contacts the substrate.
With a substrate holder having such an electrical contact, since the metal contact plate constituting the electrical contact is generally of a rigid body, the contact plate makes point contact with a substrate, and therefore, poor contact is likely to occur. Further, the metal contact plate contacts the substrate at a position somewhat inside a periphery of the substrate, which narrows an effective area for pattern formation in the substrate.
In addition, substrates and members generally vary in size. Due to this size variation and also to a positional relationship between a pair of supports, positioning (centering) of a substrate to be held by the supports with respect to a sealing member mounted to one of the supports is generally difficult. A separate provision of a special member for positioning of a substrate leads to a large-sized and complicated substrate holder.
Furthermore, according to the conventional substrate holder, a sealing member is mounted to one of a pair of supports and the sealing member is brought into pressure contact with a peripheral portion of a substrate placed and held on the other support, thereby sealing the peripheral portion of the substrate, as described above. There is, therefore, a case where when opening the support, to which the sealing member is mounted, to take the substrate out of the substrate holder after completion of plating, the support opens with the substrate sticking to the sealing member and the substrate falls from the support. Measures must therefore be taken to solve this problem.